Demographic characteristics and risk factors related to high blood pressure among healthy blood donors from Luanda, Angola: A retrospective study

Abstract Background and Aims Hypertension is a public health concern, mainly in resource‐limited countries. We investigated the characteristics and risk factors related to high blood pressure in healthy blood donors from, Luanda, the capital city of Angola. Methods This was a retrospective study that included 343 healthy donors from December 2019 to September 2020. Results The mean age was 32 ± 9 years. Men represented 93% of the population. Mean systolic blood pressure (SBP) was 131 ± 12.3 mmHg (ranging from 100 to 160 mmHg) and diastolic blood pressure (DBP) was 80.1 ± 9.72 mmHg (from 56.0 to 100 mmHg). DBP was related to age and gender (p < 0.05). About 7.3% of the donors had high‐pressure (>140/90 mmHg). Age between 20 and 40 years (odds ratio [OR]: 2.52, p = 0.043), women (OR: 1.87, p = 0.548), nonurbanized areas (OR: 0.39, p = 0.067), high educational level (OR: 0.76, p = 0.637), employed (OR: 0.49, p = 0.491), voluntary donors (OR: 0.87, p = 0.799), blood group B (OR: 2.06, p = 0.346), and Rh‐ (OR: 0.26, p = 0.104), were potentially related with high‐pressure. The high‐pressure cases increased from December 2019 (4%) to September 2020 (28%) (p = 0.019). Conclusion We showed high pressure among the healthy blood donors population. Demographic characteristics, ABO/Rh blood group, and year period are features that should be considered in cardiovascular disease control strategies. Biological and nonbiological features related to blood pressure changes should be considered for further studies in the Angolan population.


| INTRODUCTION
High blood pressure is one of the greatest global public health concerns affecting approximately one billion individuals worldwide 1 and constitutes the main risk factor for coronary heart disease, heart failure, cerebrovascular disease as well as chronic renal failure, [2][3][4] besides being responsible for about 30% of deaths worldwide annually. 5,6 The World Health Organization (WHO) estimated that low-and middle-income countries (LMICs) have 93% of the world's disease burden and contributed to about 78% of deaths from cardiovascular disease and more than 50% of the total disease burden. 7 If nothing is done to reduce the risk of chronic diseases in resource-limited countries, an economic production estimated at US$ 84 billion will be lost to heart disease, stroke, kidney disease, and diabetes. 8 This finding showed that high blood pressure is an essential feature of the epidemiological transition, although some studies have shown that there are no significant differences in the mean prevalence of hypertension between developed and developing countries. 9,10 However, it is worth mentioning here that the health profile of many LMICs, such as Angola, is undergoing major changes due to diet and lifestyle changes, 11 therefore, with the increase in life expectancy diseases of old age are also increasing, including hypertension and cardiovascular disease, as previously described the relationship between old age and cardiovascular disease. 12 These findings show that it is necessary to identify which biological or nonbiological characteristics might be influencing the emergence of healthy people with early diagnosis of high blood pressure, mainly in LMICs.
Since the 1990s, evidence has grown on the relative importance of systolic or diastolic blood pressure alone and together, on cardiovascular events. 13 Currently, there are no published studies that describe the mean systolic or diastolic blood pressure, in the healthy population over 18 years of age in Angola. To the best of our knowledge, voluntary blood donors are the source of all red cell, platelet, and unprocessed plasma products used in clinical medicine. 14 Therefore, in this study, we investigated the putative biological and nonbiological features that could affect blood pressure levels in the healthy population in Luanda, the capital city of Angola. The results of this study might be used by decisionmakers to reinforce ongoing practice guidelines 15 for the management of arterial hypertension and cardiovascular diseases in Angola.

| Study design and setting
This was a retrospective multicentre cohort study that included 343 subjects who were assessed as healthy for blood donation at the Instituto Nacional de Sangue and Clínica Girassol, both health units located in Luanda, the capital city of Angola, between December 3 | RESULTS

| Demographic characteristics related to high blood pressure
The putative demographic characteristic related to high blood pressure among blood donors from Luanda is summarized in From December 2019 to September 2020, the systolic (from 130 ± 11.7 to 136 ± 11.1 mm/Hg, p = 0.026) and diastolic (from 78.9 ± 9.13 to 83.3 ± 9.67 mm/Hg, p < 0.001) blood pressure indexes increased significantly. Moreover, we observed a significant increase in the rate of blood donors with high blood pressure increased significantly (p = 0.019) from 4% in December 2019 to 28% in September 2020. A higher rate of high blood pressure in blood donors was observed in January 2020 (32%, 8/25). Also, during this period blood donors were 2.5 times (95% CI: 0.86-7.25, p = 0.093) more likely to develop high blood pressure.

| ABO/RH blood group and high blood pressure
The relationship between ABO/Rh blood groups with high blood pressure among blood donors from Luanda is shown in Table 2  Previous studies showed that the blood donation candidate can only be approved when at least the maximum systolic blood pressure is below 140 mmHg and the diastolic below 90 mmHg. 12,15,18 The mean values of systolic (131 ± 12.3 mmHg) and diastolic (80.1 ± 9.72 mmHg) pressure in our study correspond with the global blood pressure norms for the healthy population (Table 1). However, it is worth mentioning that the maximum systolic blood pressure was 160 mmHg and the maximum diastolic blood pressure was 100 mmHg, suggesting that some blood donors from Angola, a sub-Saharan African country, are experiencing high blood pressure and risk of developing stroke, myocardial infarction, heart and/or renal failure, 2-4 even before donating at least 450 mL of whole blood.
Previous studies carried out independently contributed to a universal discovery in which reducing blood pressure levels in the general population remarkably reduces cardiovascular morbidity and mortality, as well as slowing the progression of kidney disease, retinopathy, and death from all causes. 1,19 Therefore, further studies assessing  of the hypertensive population were female. 5 Furthermore, a study comparing the hypertensive population of Portugal and immigrants from the portuguese speaking African countries, revealed that 51% and 67% of the population in both groups were hypertensive women from Portugal and immigrants, respectively. 25 The physiological aspects such as hormonal climacteric changes, menopause, menstruation, pregnancy, and breastfeeding inherent to the female gender could explain the reduced participation of females in blood donation as well as being a factor for present high blood pressure.
The large adhesion of blood donors during January 2020 is not surprising, and the possible explanation is that once in this period, Luanda province like other Angola provinces, face heavy rainfall, and due to poor sanitation, there is an increase in stagnant water and thus increases also the circulation of vectors capable of increasing cases of malaria, dengue, or other vector-borne diseases in Luanda, as verified by other studies. 22,[26][27][28][29] However, the increase in malaria and dengue cases could be one of the reasons for the increase in blood donation since many patients with malaria or dengue need blood transfusions during hospital treatment. 30  to be more susceptible to hypertension. 32 In this study, we did not explore the reasons why blood group B individuals present a higher risk of developing high blood pressure, despite the decline in frequency in the Angolan population. Therefore, further studies assessing the possible biological or nonbiological factors that could influence systole or diastole blood pressure values in the general population, especially those belonging to blood group B, must be carried out.
This study has some potential limitations. Firstly, the small sample size of participants limited the significance of our results and may not be representative of the whole Angolan population.
However, to obtain an updated and more representative picture of the hypertension situation in the healthy Angolan population, it is important to gather the most recent data and quantify the rate of high blood pressure in the healthy population from the different regions of Angola. Second, a family history of hypertension or chronic disease, especially in the donor population with high blood pressure, was not obtained or described in this studied population.
Finally, a follow-up and assessment of blood pressure after blood donation or clinical outcome (recovered or deceased) whether from the blood donor after blood donation or the patient after receiving the blood component, was not performed on all blood donors included in this study, which limits the retention of the strong conclusion if these donors were hypertensive or the high blood pressure values were due to a clinical or psychosocial condition. Despite these weaknesses, our findings provide an important description of the mean values of systolic and diastolic blood pressure in the healthy population from Angola. Therefore, must be carried out further studies including epigenetic, sociodemographic, behavioral, clinical, and eating features, as well as, a description of the clinical reasons for carrying out the donation in the case of family donors. Also, studies assessing blood pressure postblood donation over some time including laboratory tests to assess cardiac, hepatic, or renal function, should be considered for future investigation. These studies could provide a specific picture of which population should adhere more to the primary prevention measures of hypertension, involving actions at the community level such as reducing obesity, consumption of alcohol and salt as well as increased physical activity. 15